(1) Field of the Invention
This invention concerns a process for producing a phosphoric ester salt of high purity.
(2) Description of the Prior Art
Phosphoric ester salts of organic hydroxy compounds have been used in a wide variety of fields such as detergents, rust preventives, emulsifying agents, textile processing aids, liquid ion exchange materials and pharmaceuticals.
There have been known various processes for producing phosphoric esters including, for example, (1) a method of using phosphorus oxychloride and an organic hydroxy compound, (2) a method of using phosphorus pentoxide, water and an organic hydroxy compound (Japanese Patent Publication No. 61358/1982), or (3) a method of using orthophosphoric acid or polyphosphoric acid and an organic hydroxy compound (Japanese Patent Publication No. 38435/1983, A. K. Nelson et al, Inorganic Chemistry 2, 775 (1963) and Japanese Patent Publication No. 26492/1968).
However, in the phosphates thus produced are generally included impurities, which are nonionic compounds such as unreacted organic hydroxy compounds, impurities and coloring ingredients in the organic hydroxy compounds or by-products resulted in the phosphorylating process. For instance, in method (1), alkyl chlorides are by-produced, and in method (2), the objective phosphate is accompanied by the presence of unreacted organic hydroxy compounds and decomposed products of phosphates. Further, in method (3), a great amount of orthophosphoric acid is by-produced besides these nonionic impurities. Although some of the present inventors have proposed a method of industrially removing orthophosphoric acid from a mixture of phosphate and orthophosphoric acid by using a solvent (Japanese Patent Application Laid-open No. 258191/1985), nonionic compounds can not be removed even by this method.
Nonionic impurities in the phosphates cause the final phosphoric ester salts to have peculiar odors, undesirable color or to be stimulative. Depending on the application of the phosphoric ester salt, such problems remarkably reduce the commercial value of the products.
Among all, in the case of using a phosphoric ester salt as a material for cosmetics such as creams or hair conditioners, detergents such as shampoos, cleansing creams and bath agents, as well as tooth pastes which are directly used to or in contact with a human body, these impurities provides a serious defect in these commercial products. Accordingly, when the phosphoric ester salt is incorporated into such products, removal of the impurities in the phosphoric ester is extremely important.
One of the methods of removing the nonionic impurities in the phosphoric esters is to recrystallize or to extract the phosphoric ester by using a solvent. This method, however, requires a great amount of solvent for the phosphoric ester to recrystallize, which inevitably makes loss of the phosphoric ester in the solvent, although the nonionic ingredients are removed. Further, in case where the phosphoric ester is a mixture of mono- and diesters, or in case where the phosphoric ester is prepared by phosphorylating an oxo-alcohol having a distribution in the alkyl chain length in the organic hydroxyl compound, the composition of the phosphoric esters changes by recrystalization. Further, the method can not be applied to non-crystalline phosphoric ester. Furthermore, it is very difficult to separate and remove only the nonionic ingredients from the phosphoric ester by extraction in case where the phosphoric ester is in the acidic form. The system is liable to be emulsified in the method of extracting the phosphoric ester in the form of a salt into an aqueous layer and extracting the nonionic ingredients into the organic layer.
As a method of deodorizing the organic phosphate, there has been known a method of forming a thin liquid film of the phosphoric ester and bringing the film into contact with an inert gas (Japanese Patent Application Laid-Open No. 35595/1982). However, this method can only be applied to the phosphoric ester which is liquid at a temperature of 60 to 90.degree. C and can remove only the nonionic ingredients having a low boiling point.
Accordingly, there has been a need for the development of a process capable of removing unreacted organic hydroxy compounds, impurities or coloring ingredients in the organic hydroxy compound from the phosphoric ester, and nonionic compounds by-produced in the phosphorylating process with industrial ease and economical advantage.